Recently, proposed is a system to authenticate alteration of image data generated by an image sensing apparatus such as a digital camera as disclosed in U.S. Pat. No. 5,499,294 (hereinbelow, US'294) and Japanese Published Unexamined Patent Application No. 2002-244924 (hereinbelow, JP'924).
Further, Japanese Published Unexamined Patent Application No. 2001-78142 (hereinbelow, JP'142) discloses an apparatus which prohibits alteration of the contents of an image file if image-file authentication data is embedded in the image file. The authentication data means data necessary for determining whether or not the image file has been altered. The data is defined as “feature data” in JP'142.
However, in the apparatus in JP'142, as alteration of the content of image file with authentication data is prohibited, the contents of the image file, even if require alteration, cannot be altered. Further, if the image file with authentication data is altered, it is determined that the original of the image file has been altered.